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Congratulations, your rat has just qualified for the two year club (or for
that matter, the 18 month milestone). While this may be a laudable
accomplishment on the rat's part, a responsible rat owner has to be on the
lookout for medical problems. Although elderly rats are more commonly
afflicted with respiratory illness and tumors (usually mammary), the
incidence of paralysis is also quite high. Causes for paralysis are numerous,
and, like respiratory infection and tumors, early detection can minimize
suffering for you and your rat.
PARALYSIS: THE MAJOR PLAYERS
Okay, so you suspect your elderly rat may have weakness. What are the
possible causes, treatments, and prognoses? The list of possibilities is
extensive; however, it can usually be narrowed down to three major players:
stroke, pituitary adenoma, and spinal compression due to vertebral
degeneration. Two factors help to distinguish among these disorders.
Generally, only stroke will present with an acute onset, so it's important to
observe how suddenly the weakness has occurred. Second, note the pattern of
the weakness. Are the forelimbs primarily affected? Is one side of the body
weak?
STROKE
Strokes are fairly common in elderly rats, and may be the most treatable
cause of paralysis. As mentioned, paralysis due to stroke is sudden. Your
perfectly healthy rat may be frolicking with cagemates one day and be
stricken the next. Due to the anatomy of the nervous system, stroke commonly
affects one side of the body, but not always.
Stroke is caused by the interruption of blood flow to the brain or spinal
cord. This may happen in one of two ways. First, a blood clot can plug
vessels, starving nervous tissue, or a vessel can rupture causing bleeding.
It is for this second reason that preventive treatment with aspirin (or other
anticoagulants) is controversial and generally not recommended. The extent of
damage will depend upon the size and location of the area affected. Strokes
to the motor areas of the brain will cause the one-sided weakness noted
above. More ominous are strokes that affect the brainstem, which contains
areas vital for life, such as heart and respiratory centers. Brainstem
strokes may cause a head tilt, as balance is mediated by this brain region.
MILD WEAKNESS
Since our rats cannot talk to us and emotional changes are difficult to
detect, the first signs of central nervous system damage will be motor, that
is, difficulty moving or coordinating movement. Identifying moderate or
severe paralysis is straightforward. The rat has trouble moving, cannot groom
himself, and certainly cannot keep up with healthy cagemates. A number of
conditions causing weakness in rats exhibit a gradual onset, therefore it is
possible and advantageous to recognize (and treat) mild weakness as soon as
possible.
Weakness in its earliest stages may manifest as clumsiness. Your rat will
lose his grip on the wall of his wire cage, or may pratfall off objects in
his home, such as cardboard boxes or ladders. A reluctance to climb by a
formerly active rat may also be an indication of weakness. A rat with mild
forelimb weakness may have trouble holding food (he is unable to curl his
fingers around the food), and may contort himself during feeding. For
instance, he may hunch over so that food is wedged securely between his body
or the floor of the cage and his weak limb. During excursions outside his
cage, watch your rat walk. Weak hindlimbs may cause the rat's back feet to
slip, giving him the appearance of walking on an icy surface. In contrast, a
rat favoring an injured limb will tend to lift it, sparing pressure from body
weight. A weak rat, of course, is unable to lift the limb.
PITUITARY ADENOMA
This is usually a benign tumor of the pituitary gland, which is situated at
the base of the brain. Pituitary tumors primarily affect older female rats.
The location makes the tumor inoperable, and the compression of nearby brain
tissue likely. In contrast to strokes, the onset of weakness in an expanding
pituitary mass is gradual. Commonly, the forelimbs will become weak first,
and the rat will have trouble holding food. Weakness can then spread to the
hindlimbs. Pituitary tumors carry a poor prognosis, but early treatment with
prednisone can temporarily relieve symptoms. In addition, there has been some
evidence that antibiotics can shrink tumors, and these may be added to the
treatment regimen. Perhaps the best treatment for pituitary tumors is
preventive. These are hormone-driven tumors, as are mammary tumors, therefore
spaying greatly reduces their incidence. Spaying rats, of course, is a
controversial and risky procedure, and not all rat owners condone it.
VERTEBRAL COMPRESSION
As a rat (or human, for that matter) ages, connective tissue such as
cartilage degenerates. Vertebrae, the bones of the spinal column, are
separated by pads of cartilage. When these degenerate, the vertebrae collapse
on one another and the vertebral canal, where the spinal cord passes, can
become narrow. (Or a disc can herniate from an unstable vertebral column and
have the same effect.) The spinal cord may be compressed and cause weakness.
Weakness from vertebral degeneration commonly affects the lower spine, and
hindlimbs on both sides may be involved. Forelimb weakness may be caused by
compression of upper regions of the spinal cord, which is less common. As
with pituitary tumors, weakness is gradual in onset. Prednisone helps to
minimize compression and any swelling due to arthritis, which is actually
quite rare in rats.
THE ZEBRAS
In medicine, "zebras" are rare causes of common symptoms. Regarding weakness
in rats, zebras may include infection of the central nervous system
(mycoplasma has been known to infect the brain), including abscesses, which
may behave like growing tumors. Spinal cord tumors have also been observed in
rats. A rare case of metabolic disorder causing weakness has also been
reported. In this rat, specific foods (such as broccoli) could not be
properly metabolized, resulting in severe paralysis. Ingestion of toxins may
also cause central nervous system damage, as will overdosing with certain
drugs (such as Ivermectin).
IN CONCLUSION
The major causes of paralysis in rats can be treated with the
anti-inflammatory agent, prednisone. Note that prednisone has its drawbacks,
namely side effects, a major one being possible diabetes. Severe weakness
will require nursing care, including bathing and feeding. Separation from
cagemates may be necessary, depending on how the other rats are responding to
the sick one. It is, of course, up to the owner to decide when and if to
euthanize a gravely ill rat, paralyzed or not.
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